1. Field of the Invention
The present invention relates to an electro luminescence (EL) panel, and particularly, to a hybrid electro luminescence panel having characteristics such as high brightness, a large size, long life span, and easy control of color balance using advantages of an organic EL and an inorganic EL.
2. Description of the Background Art
Generally, an electronic display device is an electric device for changing electric information signals outputted from various electric devices to light information signals which are visible.
The electronic display device is able to display the light information signals as patterned information such as numbers, characters, figures, and pictures (hereinafter, referred to as image), and can be divided into an emissive display device displaying the light information signal by self-emission, and a non-emissive display device display the light information signal by controlling peripheral lights such as reflection, dispersion, and interference phenomenon.
There are the emissive display devices such as field emission display (FED), vacuum fluorescent display (VFD), electro luminescence (EL), and plasma display panel (PDP), and there are the non-emissive display devices such as liquid crystal display (LCD), and electro chromic display (ECD).
The EL device among above various electronic display devices is one of the most highlighted devices.
The EL device has a structure that a phosphor is inserted between two electrodes, and it is the display device using a phenomenon that electrons released from the electrodes when a voltage is applied are crashed to the phosphor to generate charge and discharge and to emit the light.
The EL device can be divided into an organic EL device and an inorganic EL device according to materials used and structure.
FIG. 1 is an exemplary view showing a cell structure of a general inorganic EL device.
As shown therein, the inorganic EL device comprises: a phosphor layer 7 formed between a transparent electrode 11 and a rear electrode 3; a lower insulating layer 5 and an upper insulating layer 9 formed on upper and lower parts of the phosphor layer 7 respectively; and a glass substrate 13 formed on rear surface of the transparent electrode 11. Herein, the upper and lower insulating layers 9 and 5 are formed using dielectric substances. Therefore, when the voltage is applied from outer side, the upper and lower insulating layers 9 and 5 have predetermined capacitance values.
A luminescent layer 7 is formed using inorganic substances such as ZnS and Mn. The rear electrode 3 is formed using conductive substance such as Al. Herein, the rear electrode 3 is used as a scan electrode for supplying a scan pulse to the cells 1. The transparent electrode 11 is formed by a transparent conducting substance such as indium-tin-oxide (ITO). Herein, the transparent electrode 11 is used as a data electrode for supplying data to the cells 1.
After that, when the voltage is applied between the rear electrode 3 and the transparent electrode 11, a hole is accelerated toward the rear electrode 3 and the electron is accelerated toward the transparent electrode 11. Therefore, the electron and the hole are crashed into each other on center portion of the emissive layer 7, and thereby visible light is generated to display a predetermined image.
FIG. 2 is an exemplary view showing a cell structure of a general organic EL device.
As shown therein, the organic EL device comprises: a metal electrode 23 and a transparent electrode 35; a luminescent layer 29 formed between the metal electrode 23 and the transparent electrode 35; an electron injecting layer 25 and an electron transporting layer 27 formed between the luminescent layer 29 and the metal electrode 23; and a hole injecting layer 33 and a hole transporting layer 31 formed between the luminescent layer 29 and the transparent electrode 35.
The metal electrode 23 is formed using a conductive substance such as Al, and used for supplying the scan pulse to the cells. The transparent electrode 35 is formed using a transparent conductive substance such as the ITO, and used for supplying the data to the cells. The electron injecting layer 25 supplies the electron provided from the metal electrode 23 to the electron transporting layer 27. The electron transporting layer 27 supplies the electron provided from the electron injecting layer 25 to the luminescent layer 29 after accelerating the electron. The hole injecting layer 33 supplies the hole provided from the transparent electrode to the hole transporting layer 31. And the hole transporting layer 31 supplies the hole provided from the hole injecting layer 33 after accelerating the hole.
After that, when the voltage is applied between the metal electrode 23 and the transparent electrode 35 from the outer side, the hole generated on the transparent electrode 35 is accelerated toward the metal electrode 23, and the electron generated on the metal electrode 23 is accelerated toward the transparent electrode 35. Therefore, the hole provided from the hole transporting layer 31 and the electron provided from the electron transporting layer 27 are crashed into each other on center portion of the luminescent layer 29, and thereby, the visible light is generated to display a predetermined image.
FIG. 3 is an exemplary view showing a general inorganic or organic EL matrix panel.
As shown therein, the inorganic or organic EL matrix panel comprises: pixel cells 1 and 21 located on crossed areas of data lines D1, D2, . . . , Dn and scan lines S1, S2, . . . , Sm; a data driving unit 51 for supplying the data pulse to the data lines; a scan driving unit 41 for supplying the scan pulse to the scan lines; and a panel 61 on which the data lines, the scan lines, and the cells are installed.
The scan driving unit 41 supplies the scan pulse to the scan line in order. The data driving unit 51 supplies the data pulse synchronized with the scan pulse to the data line. At that time, the pixel cells 1 and 21 which receives the scan pulse and the data pulse are turned on when the voltage is larger than a threshold voltage which is set in advance, and turned off when the voltage is smaller than the threshold voltage. Therefore, the pixel cell displays the image by releasing the visible light corresponding to the inputted data pulse.
However, the above inorganic EL panel has a different threshold voltage of the phosphor due to the characteristics of the phosphor, that is, constructing the luminescent layer using the inorganic substance. Therefore, the inorganic EL panel may have problems such as lack of saturation, lack of brightness, and wrong discharge when the same driving voltage is applied in realizing the colors of red, green, and blue. Also, the blue color phosphor has a shorter life span than those of the red and green color phosphors, and has a lower brightness. Therefore, it is difficult to set the color balance in the inorganic EL panel due to the brightness lowering of the blue color phosphor.
On the other hand, the general organic EL panel needs high electric current when driving, and it is difficult to scale up due to chromaticity lowering according to temperature. Also, the red color phosphor in which the luminescent layer is constructed using the organic substance has shorter life span than those of the blue and green color phosphors, and has lower brightness. Therefore, it is difficult to set the color balance in the organic EL panel due to the brightness lowering of the red phosphor.